DE 39 25 280 has disclosed a cooling plate in which the cooling passages are formed by pipes cast into cast iron. The bearing lug is also connected to the cooling system. The dissipation of heat from these plates is low on account of the low thermal conductivity of the cast iron and on account of the resistance between the cooling pipes and the plate body caused by a layer of oxide or an air gap.
In the event of a loss of the blast furnace refractory lining after a certain operating time, the inner surface of the cooling plates is directly exposed to the temperature of the furnace. Since the furnace temperature is well above the melting point of cast iron and the inner heat transfer resistances of the cooling plates lead to unsatisfactory cooling of the hot side of the plates, accelerated wear of the cast iron plates is inevitable and the service life is correspondingly limited.
DE 199 43 287 A1 has disclosed a copper cooling plate which, in the vicinity of the upper coolant pipe sections, is fixedly connected to the furnace casing by means of a fixed-point securing element. In addition, the upper coolant pipe sections are likewise fixedly connected to the furnace casing. Further securing elements are designed as movable-point securing elements which allow mobility in both the horizontal direction (x) and in the vertical direction (y). The lower coolant pipe sections are connected in a gastight manner to the furnace casing only by means of standard compensators. Therefore, in this region the cooling plate is not fixed in any of the three spatial directions.
On account of the fact that the side of the cooling plate which faces the interior of the furnace reaches temperatures of more than 300° C. and the side which faces the furnace casing remains at coolant temperature, i.e. approximately ambient temperature, the cooling plate is exposed to very high thermally induced stress forces. In the cooling plate described in DE 199 43 287 A1 this means that the plate, which is of course completely fixed at a number of locations, is plastically deformed under the influence of heat and during cooling bulges into the interior of the furnace in the shape of a dish. This leads to cracks in the coolant pipe sections and to coolant leaks.